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United States Patent |
6,143,912
|
Lindner
,   et al.
|
November 7, 2000
|
Process for preparing methylhydrogenpolysiloxanes having trimethylsilyl
end groups
Abstract
A process for preparing methylhydrogenpolysiloxanes having trimethylsilyl
end groups wherein, in a first step, methyldichlorosilane and
trimethylchlorosilane are reacted with at most 0.5 mol of water per mole
of hydrolyzable chlorine to give a partial hydrolysate and gaseous
hydrogen chloride and, in a second step, the partial hydrolysate, to
remove the SiCl groups still present, is treated with water, forming
hydrochloric acid.
Inventors:
|
Lindner; Tassilo (Mehring-Od, DE);
Geisberger; Gilbert (Altotting, DE);
Pachaly; Bernd (Mehring-Od, DE)
|
Assignee:
|
Wacker-Chemie GmbH (Munich, DE)
|
Appl. No.:
|
318412 |
Filed:
|
May 25, 1999 |
Foreign Application Priority Data
| Jun 25, 1998[DE] | 198 28 390 |
Current U.S. Class: |
556/451; 508/207; 525/474; 528/31; 528/499; 556/456 |
Intern'l Class: |
C08G 077/06; C08G 077/12 |
Field of Search: |
556/451,456
508/207
528/31,499
525/474
|
References Cited
U.S. Patent Documents
2491843 | Dec., 1949 | Wilcock.
| |
2758124 | Aug., 1956 | Schwenker.
| |
4382145 | May., 1983 | Yeboah.
| |
Foreign Patent Documents |
1 125 180 | Mar., 1962 | DE.
| |
2 104 906 | Mar., 1983 | GB.
| |
Primary Examiner: Dawson; Robert
Assistant Examiner: Peng; Kuo-Liang
Attorney, Agent or Firm: Brooks & Kushman P.C.
Claims
What is claimed is:
1. A process for preparing methylhydrogenpolysiloxanes having
trimethylsilyl end groups, said process comprising:
in a first step, reacting methyldichlorosilane and trimethylchlorosilane
with at most 0.5 mol of water per mole of hydrolyzable chlorine to give a
partial hydrolysate and gaseous hydrogen chloride, and
in a second step, treating the partial hydrolysate with water to remove the
SiCl groups still present, forming hydrochloric acid.
2. The process as claimed in claim 1, wherein, hydrochloric acid formed in
the second step is used as a water source in the first step.
3. The process as claimed in claim 1, wherein the
methyldichlorosilane:trimethylchlorosilane weight ratio is from 100:1 to
2:1.
4. The process as claimed in claim 2, wherein the
methyldichlorosilane:trimethylchlorosilane weight ratio is from 100:1 to
2:1.
5. The process as claimed in claim 1, wherein both steps are carried out
fully continuously.
6. The process as claimed in claim 2, wherein both steps are carried out
fully continuously.
7. The process as claimed in claim 3, wherein both steps are carried out
fully continuously.
8. The process as claimed in claim 1, in which high-volatility constituents
are separated off downstream of the first and/or second step and these
high-volatility constituents are recycled to the first and/or second step.
9. The process as claimed in claim 2, in which high-volatility constituents
are separated off downstream of the first and/or second step and these
high-volatility constituents are recycled to the first and/or second step.
10. The process as claimed in claim 3, in which high-volatility
constituents are separated off downstream of the first and/or second step
and these high-volatility constituents are recycled to the first and/or
second step.
11. The process as claimed in claim 4, in which high-volatility
constituents are separated off downstream of the first and/or second step
and these high-volatility constituents are recycled to the first and/or
second step.
Description
TECHNICAL FIELD
The invention relates to a process for preparing
methylhydrogenpolysiloxanes having trimethylsilyl end groups from
methyldichlorosilane, trimethylchlorosilane and water.
BACKGROUND ART
In U.S. Pat. No. 2,758,124, methyldichlorosilane and trimethylchlorosilane
are reacted with a large excess of water to produce
trimethylsilyl-terminated methylhydrogenpolysiloxanes. However, the
process is difficult to control and leads to branching in the polysiloxane
chain or even gelling of the product. HCl generated appears as
hydrochloric acid.
DE-A-1 125 180 describes a process in which, in a first step,
methyldichlorosilane and trimethylchlorosilane are hydrolyzed with 1 mol
of water per mole of hydrolyzable chlorine in concentrated hydrochloric
acid. The concentrated hydrochloric acid contains tetrahydrofuran. In a
second step, the crude hydrolysate is admixed with a large amount of
water. The oil thus produced is resistant to gelling. However, in this
process, large amounts of tetrahydrofuran-containing concentrated
hydrochloric acid, as well as dilute hydrochloric acid occur, neither of
which can be economically reworked.
DISCLOSURE OF INVENTION
The object underlying the invention is to provide a process for preparing
methylhydrogenpolysiloxanes having trimethylsilyl end groups, in which
process no branching is formed in the methylhydrogenpolysiloxane and in
which a high proportion of the chlorine of the starting material occurs as
HCl gas.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of a continuous process for preparing
methylhydrogenpolysiloxanes according to one embodiment of the subject
invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a process for preparing
methylhydrogenpolysiloxanes having trimethylsilyl end groups, in which
process in a first step, methyldichlorosilane and trimethylchlorosilane
are reacted with at most 0.5 mol of water per mole of hydrolyzable
chlorine to give a partial hydrolysate and gaseous hydrogen chloride, and,
in a second step, the partial hydrolysate, to remove the SiCl groups still
present, is treated with water, forming hydrochloric acid.
The hydrolyzable chlorine is present in the form of SiCl groups.
Preferably, in the first step, at least 0.3 mol of water is used per mole
of hydrolyzable chlorine.
The partial hydrolysate formed in the first step consists of Cl-terminal
and trimethylsilyl-terminal, and optionally OH-terminal, hydrogen
methylpolysiloxanes and cyclic hydrogenmethylpolysiloxanes.
The content of SiCl groups still present in the partial hydrolysate is
preferably from 0.5 to 5% by weight, in particular from 1.0 to 2% by
weight.
The hydrogen chloride gas occurring in the first step can be used directly
in another process, for example with methanol to prepare chloromethane,
which in turn is used in methylchlorosilane synthesis. Thus, the chlorine
can be recycled, without being given off to the environment.
In the second step, the chlorine content of the partial hydrolysate is
completely reacted with water. The hydrochloric acid thus formed
preferably has an HCl content of from 3 to 20% by weight, in particular
from 5 to 10% by weight.
In a particular embodiment, hydrochloric acid formed in the second step is
used as a water source in the first step. Preferably, at least 90%, in
particular at least 95%, of hydrochloric acid formed in the second step is
used in the first step.
In the first step, the hydrochloric acid formed in the second step is then
completely converted to gaseous hydrogen chloride and partial hydrolysate
and thus consumed.
In a particularly preferred embodiment, in the second step, the amount of
water used is at most sufficient so that the water of the hydrochloric
acid formed is completely converted in the first step.
The chain lengths and viscosities of the methylhydrogenpolysiloxanes
prepared are controlled via the methyldichlorosilane:trimethylchlorosilane
weight ratio used. The methyldichlorosilane:trimethyl-chlorosilane weight
ratio is preferably from 100:1 to 2:1, in particular from 50:1 to 5:1.
The second step of the process according to the invention is preferably
carried out at a temperature of from 0 to 100.degree. C., in particular
from 10 to 60.degree. C.
The process according to the invention can be carried out batchwise,
semicontinuously or fully continuously, preferably by a fully continuous
procedure in both steps, for example in a loop reactor, in particular in a
linked plant.
In a particular embodiment, the high-volatility constituents are separated
off after the first and/or the second step. The high-volatility
constituents are principally cyclic methylhydrogensiloxanes and, if
appropriate, solvent. This embodiment is preferred for preparing
low-volatility methylhydrogenpolysiloxanes having trimethylsilyl end
groups. Preferably, the high-volatility constituents are recycled to the
first and/or second step, in particular to the first step.
Preferably, when the high-volatility constituents are being separated off,
the amount of substance separated off is replaced by an organic solvent.
Preference as an organic solvent is given to toluene.
The separation of the high-volatility constituents can serve to produce
cyclic hydrogen methylpolysiloxanes.
FIG. 1 shows a preferred embodiment of the process according to the
invention:
In the first step, methyldichlorosilane and trimethylchlorosilane are fed
into the loop reactor (1) via line (5), hydrochloric acid is fed via line
(10) and the distillate from the thin-film evaporator (4) is fed in via
line (12). Gaseous hydrogen chloride is removed via line (6) and the
partial hydrolysate prepared is removed via line (7).
The partial hydrolysate is metered into the loop reactor (2) via line (7)
and water is metered into the loop reactor (2) via line (8).
All of the reaction mixture is thereafter fed into a separator (3) via line
(9). There, the hydrochloric acid is separated off as lower phase and is
recirculated to the loop reactor (1) via line (10). The upper phase is fed
into the thin-film evaporator (4) via line (11). The high-volatility
constituents are recirculated to the loop reactor (1) via line (12). The
effluent (13) comprises the methylhydrogenpolysiloxanes having
trimethylsilyl end groups. In the following examples, the reference
numbers relate to FIG. 1
EXAMPLE 1
(according to the invention)
130 kg/h of methyldichlorosilane and 7.0 kg/h of trimethylchlorosilane are
fed into the loop reactor (1) via line (5), 60 l/h of distillate of the
thin-film evaporator (4) (comprising 30% by weight of low-molecular-weight
methylhydrogensiloxanes and 70% by weight of toluene) are fed in via line
(12) and hydrochloric acid from separator (3) is fed in via line (10) at
30.degree. C. The resultant hydrogen chloride is taken off from the
reactor in the gaseous state. The partial hydrolysate exiting from the
loop reactor (1) is passed, as a homogeneous phase having a chlorine
content of 15 g/kg, via line (7) into the loop reactor (2), where it is
mixed with 21.5 kg/h of water.
The reaction mixture exiting from the loop reactor (2) is fed via line (9)
into the separator (3), where separation takes place into the upper
organic hydrolysate phase and the lower aqueous phase which corresponds to
an approximately 6% strength by weight hydrochloric acid. The lower phase
is recirculated to the loop reactor (1) via line (10). The organic
hydrolysate phase is dried by heating in the thin-film evaporator (4) at
130.degree. C. and 10 mbar (absolute). The resulting distillate is fed
completely into the loop reactor (1). 73 kg/h of
methylhydrogenpolysiloxane having trimethylsilyl end groups are obtained
as effluent (13) from the thin-film evaporator (4). This
methylhydrogenpolysiloxane has a chlorine content of 2 mg/kg and a
viscosity of 25 mm.sup.2 /s.
EXAMPLE 2
(according to the invention)
Example 1 is repeated with the change that 12.0 kg/h of
trimethylchlorosilane instead of 7.0 kg/h are fed into the loop reactor
(1) and 22.4 kg/h instead of 21.5 kg/h of water are fed into the loop
reactor (2). 76.5 kg/h of methylhydrogenpolysiloxane having a chlorine
content of 2 mg/kg and a viscosity of 15 mm.sup.2 /s are obtained.
COMPARATIVE EXAMPLE 1
(not according to the invention, with an excess of water)
Example 1 is repeated with the change that 40.0 kg/h instead of 21.5 kg/h
of water are fed into the loop reactor (2). A two-phase mixture exits from
loop reactor (1). 6 h later, gel formation is observed at the interphase
boundary, and after a further 12 h the experiment is terminated by massive
gel production.
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